You can remap this functionality, but this particular key combo doesn't seem to work.

By default it was on ctrl+3/4, and I don't think it's a wise choice as ctrl+number is good for either selecting first 10 tabs (chrome, ff), or for opening a speed dial entry (Opera=<12). I would actually like both of these functions, perhaps on alt+number and ctrl+number.

I prefer CTRL+TAB and CTRL+shift+TAB because they can be used with one hand moving the hand only slightly from its natural resting position. It also remains essentially identical on almost any keyboard. Neither of these are true for CTRL+PGUP and CTRL+PGDN.

Ctrl-Tab/Ctrl-Shift-Tab (along with other tab management keys like Ctrl-T and Ctrl-W) are nice because you can hit them using only the left hand, with the right hand remaining on the mouse.